Reheat turbine apparatus



Jan. l2, 1960 H. R. REEsE lA21-AL REHEAT TURBINE APPARATUS Filed Jan. 22, 1957 kwh Qwlwt Ok. l Nm A S N A L .mv

United States Patent C REHEAT TURBINE APPARATUS Homer R. Reese, Springfield, and Edwin G. Noyes, Jr.,

Chester, Pa., assi'gnors to Westinghouse I illectric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 22, 1957, Serial No. 635,228

1 Claim. (Cl. 253-69) This invention relates to reheat turbines and in particular to an arrangement of the elastic uid iiow path through a combined high pressure and intermediate pressure axial ow steam turbine.

In reheat steam turbines it is the practice to supply steam at a high pressure and temperature to a suitable tiow path comprising a rst group of blade rows or hlghV pressure element adapted to utilize such steam, then to circulate it through a reheater where the temperature is increased a predetermined amount, and thereafter to supply the reheated fluid to a second group of blade rows or intermediate pressure element. Heretofore, the blade rows of the high pressure element and of the intermediate pressure element have been arranged so that the flow of steam was in opposite directions. In this manner, the rotor thrust developed in one group of blade rows was utilized to balance the rotor thrust developed in the other group. In such a construction, if inadvertently or because of an emergency condition, the interceptor valve or the reheat stop valve were closed while uid ow through the blade rows of the high pressure element was sustained, the resulting unbalanced load imposed upon the thrust bearing would be greater than the normal thrust load, and the thrust bearing might be injured or fail.

It is an object of the present inventionto construct a reheat turbine such that the load upon the thrust bearing t Patented Jan. 12, 1960 foregoing manner, the high pressure and intermediate pressure elements are independently balanced.

The foregoing and other objects Vare eiected by the invention as will be apparent from the following description and claim taken in connection with the accompanying drawings, forming a part of this application, in which ing at the right-hand end encloses a suitable thrust bearing (not shown). The bearings are supported by suitable means (not illustrated) and are, in turn, supported by a foundation 19. v

The turbine comprises a high pressure element and an intermediate pressure element. The high pressure element comprises suitably supported cooperating stationary and rotating impulse blade rows 21 and suitably supported cooperating stationary and rotating reaction blade rows 23. An annular passage 22 provides communication be` tween the blade rows 21 and 23. The intermediate pressure element is divided into two portions comprising suitably supported cooperating stationary and rotating reaction blade rows 26 disposed to the right of the high pressure element, as viewed in the drawing, and suitably will not be greatly increased upon the happening of the foregoing condition.

Another object of the present invention is to provide a reheat turbine having a high pressure element and an intermediate pressure element which are independently balanced.

Heretofore, it has been the practice to circulate between the outer and inner casings of such a turbine the motive fluid prior to its reheating. It is a further object of the present invention to so circulate the motive lluid after being reheated and thereby to reduce the thermal gradient between the rotor and the casings.

`One embodiment of the present invention provides, in an axial ow steam turbine, a high pressure element and an intermediate pressure element. The high pressure'element is provided with high pressure stationary and rotating blade rows, and the thrust developed by the rotating blades is balanced by a high pressure balance piston. The uid exhaust from the high pressure element ows to a reheater and returns to the intermediate pressure element. The intermediate pressure element is divided into two portions comprising a iirst portion with stationary and rotating blade rows, and a second portion with stationary and rotating blade rows disposed in a manner Such that the ow isin a direction opposite to the liow through the first portion. In this manner, the rotor thrust of the rst portion of the intermediate pressure element tends to balance the thrust of the second portion. In addition, an intermediate pressure balance piston is provided to balance the difference in thrust developed by the two portions of the intermediate pressure element. In the supported cooperating stationary and rotating reaction blade rows 27 disposed to the left of the high pressure element. Between the impulse blade rows 21 and the reaction blade rows 27 are disposed a high pressure dummy piston 28 and an intermediate pressure dummy piston 29, both having annular orifices of a type well known in the art, and hence not illustrated in detail. Disposed between the reaction blades 23 and the reaction blades 26 is a gland 31.

The stationary blades of blade rows 21, 23 and 26 are supported by suitable blade rings 24, 25 and 30, respectively, which are connected to the inner casing 14 by means well known in the art. The stationary blades of blade rows 27 are supported by blade rings 35 which are connected to the outer casing 11 by means well known in the art.

In operation, high pressure and high temperature steam is supplied to the blade rows 21 and 23 of the high pres sure element from a suitable source (not illustrated) by inlet `conduits 32 which lare in communication with the rows 21 of impulse blades. The steam flows from left to right, as viewed in the drawing, through the impulse blade rows 21 and thereafter via passage 22 through the reaction blade vrows 23. The reaction blade rows 23 are in t communication with an exhaust annulus 33 and an outlet 34 leading to a reheater (not illustrated).

The steam is raised in temperature to a predetermined level in the reheater and is returned to the turbine through the inlet 37, which is in communication with the y blade rows 26 by means of a passage 38, flowing through the blade rows 26l from left to right. After leaving the blade rows 26, `the steam enters an yannular chamber 41 deiined by the space between the inner casing 14 and the outer casing 11. The steam in the chamber 41 ows from right to left and into the blade rows 27. The blade rows 27 are in communication with an exhaust annulus 43 which leads to a conduit 44 to which a conduit 45 may be connected for the purpose of conducting the steam to a low pressure turbine (not illustrated).

Between the high pressure balance piston 28 and the intermediate balance piston 29, an annular chamber 46 is provided which is in communication with the exhaust 33 by means'of `a 'conduit 47. Aportion of the steam intended for the blade rows 21 and 23 flows into the annular chamber `49 and thereafter through the annular briiices of the balance'rpiston 28 Jfrom right 'to left. "Some ofthe steam -which ows through the balance piston .28 enters 'the conduit `47 and-is taken out through the exhaust 33, Ywhile the Aremainder ows through the intermediate balance Ypiston 29, and vupon leaving the latter joins the fluid 'owing to the blade rows 27. Thus, as illustrated in the drawing, the steam pressure on the right-hand side of the high pressure balance piston 28 is the pressure of the steam -atthe first row of blades 21, considered in the direction of flow therethrough. The pressure in chamber 46 isthe exhaust pressure from the high pressure element, that is, the pressure in the exhaust 33, and this is .the pressure on the left-hand side of the high pressure balance piston 28 or the `right-hand side of the intermediate balance piston'29. The pressure on the left-hand side of the intermediate balance piston 29 is the pressure of the Huid before it enters the iirst blade row 27, considered in the direction -of flow.

The ldummy pistons 28 and 29 include annular rings 51 and 52, respectively, which encompass the rotor 16. The rings may be integral (as illustrated) Iand secured to the inner casing by a tongue and groove connection 53 of a type well known in the art, which provides a seal Iagainst the leakage of fluid from the chamber `46 or chamber 49 into the chamber 41.

The gland 31 comprises an annular ring 56 encompassing a portion of the rotor 16. The ring 56 is secured to the inner casing by a Vtongue 'and groove connection 57, of `a type well known in the art, for sealing the connection against leakage of fluid fromwithin the exhaust 33 tothe passage 38. Likewise, orifices (not illustrated in detail) well known in the art are provided along the rotor for a similar sealingpurpose.

The rotor thrust developed by the rotating blades of blade rows 21 and 23 of the high pressure element is balanced independently of the rotor thrust developed by the rotating blades of the 'blade rows 26 and 27 of the intermediate pressure element. The high pressure balance piston 28 is proportioned to balance the thrust of the high pressure rotating blades of the blade rows 21 and 23. That portion of the rotor 16 between the blade rows 21 and 23 constitutes `in effect one side of Ithe balance piston 28. The effective area of this side is that between lthe diameter of the rotor adjacent the inlet of the blade rows 23 and the diameter of the balance piston 28, since that portion of the rotor which is radially outwardly of the balance piston and which carries the blade rows 21 is subjected to substantially equal pressures in opposite axial directions. This side of the piston is subjected to the relatively high pressure of the motive uid in the passage 22, which biases the rotor to the left, as seen `on the drawing, in opposition -to the lower pressure in the chamber 46, which is exerted on the opposite side of the piston and biases the rotor to the right, so that the piston 28 is thus subjected lto a resulant axial thrust to the left. This resultant opposes the axial thrust imposed upon the rotor by the motive uid flowing through the blade rows 23, which is to the right Ias seen on the drawing. Preferably, the resultant thrust on the piston substantially counterbalances the resultant of the axial thrust to the right imposed by the motive fluid on the blade rows and the conical portion of the rotor on which the blades are mounted, and the Iaxial thrust to the left exerted by the fluid pressure in the chamber 33 and acting on the portion of the rotor between the blade rows 23 and the gland 31. The intermediate pressure element is proportioned so that the right-hand portion thereof develops `a thrust which is larger than that of the lefthand portion, and the excess is balanced by the intermediate pressure balance piston 29. In this manner, if the flow of'steam through the intermediate pressure element is terminated or restricted while the ow of steam through the high pressure element is sustained, no undue thrust will be imposed upon the thrust bearing since the high pressure balance piston will function to balance the thrust of the high pressure rotating blade rows.

Another l'advantage of the forego-ing construction is that the steam which flows between the inner `and outer casings in the annular chamber 41 has been previously reheated. In Aa typical installation, this reheated steam is at about 800 to 825 F. temperature. In prior constructions, the steam which was circulated in a somewhat similar manner was at 'about 500 F. Since the 'rotor temperature is about 1000 F. in both instances, it is seen that the thermal gradient has been reduced substantially, thus decreasing the stresses `arising because of expansion and contraction due to temperature diierential.

While the invention has been shown in but one form, it will be obvious to those skilled in .the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

What is claimed is:

An axial flow, elastic motive uid, reheat turbine com prising a casing structure, a rotor within said casing structure, a iirst group of rotating and stationary blade rows, said casing structure having means includ-ing a rst inlet conduit structure extending into said casing for admitting motive iluid yto said rst group of blade rows and means including an outlet conduit structure extending out of said casing for exhausting motive fluid from said rst group of 'blade rows, said rotor having a balance piston, means including `a passage `for imposing motive fluid pressures upon opposite sides of said balance piston the resultant of which pressures imposes. upon the balance piston an axial thrust that opposes Ithe axial thrust imposed upon the rotor by the motive uid passing through said first group of blade rows, second and third groups of rotating and stationary blade rows disposed on opposite sides of said iirst group of blade rows and arranged for ilow of motive fluid therethrough in opposite axial directions, so that the axial thrusts thereof tend to balance each other, and said casing structure having means including a second inlet conduit structure extending into said casing for admitting motive iiuid to said second blade group, means defining a passageway for conveying elastic motive fluid from the outlet of the second blade group to the inlet of the third blade group and means including `a second outlet conduit structure extending out of said casing for exhausting motive `fluid from the outlet of the third blade group.

References Citedl in the tile of this patent UNITED STATES PATENTS 

